In Patent document 1, a method for preparing a catalyst is disclosed, wherein a homogeneous solution containing at least one element selected from molybdenum, vanadium, phosphorous, antimony, copper and the like, a homogeneous solution containing at least one element selected from potassium, rubidium, cesium and thallium, a homogeneous solution containing at least one element selected from tungsten, beryllium, magnesium and the like, and ammonia if necessary are mixed and the resultant product is dried to obtain the catalyst.
Further, in Patent document 2, a method for producing a catalyst for use in producing methacrylic acid is disclosed, wherein the following step is included in which a solution or slurry containing at least molybdenum, phosphorous and vanadium and a solution or slurry containing ammonium compound are mixed and to the resultant solution or slurry a solution or slurry containing potassium and the like is added. Especially, an embodiment is disclosed in which ammonia water is dropped in a solution containing molybdenum, phosphorus and vanadium to mix both solutions.    Patent document 1: Japanese Patent Application, First Publication No. Hei 5-31368    Patent document 2: Japanese Patent Application, First Publication No. 2000-296336